Computer control systems are commonly used to monitor the status of plant processess. At a minimum the plant process monitoring system consists of plant process data acquisition, processing, and display on elements such as CRTs.
Data display on a CRT may include text material consisting of alphanumeric description and/or graphic symbols, static displays consisting of data independent of plant dynamics, and dynamic displays consisting of data, both measured and calculated, which are directly related to plant dynamics. Of these categories, dynamic data display is of paramount importance since it provides the plant operator with current plant status.
To provide a display of dynamic data on a CRT, plant process data are acquired via a multiplexer, processed in a computer system and usually stored in a data base memory. Dynamic data are then accessed from the data base memory by a display program and transfered to the CRT. The prevailing practice has been to periodically access and transfer the plant process data to a CRT at a fixed, prespecified time interval known as an update period. This practice is commonly referred to as continuous updating of CRT displays. With this technique, changes in plant status can be displayed only after the update period has elapsed, that is, on the next update cycle. Thus, the use of this technique does not fully meet the needs of the plant operator who often needs to know of changes in plant status immediately to prevent the occurrance of a crisis situation.
Furthermore, updating the display of all dynamic data on a CRT, including data which has not changed during an update cycle, increases the volume of data which must be accessed from the data base and transmitted to the CRT, thus increasing the computer system load. Consequently, computer system response time for data display on a CRT and the time between occurrence of an event in the plant and its indication on the CRT, is undesirability long. This adds to the time needed by the plant operator prior to taking corrective action. The probability exists in the prior art that a rapidly changing plant process variable may not be displayed at all. Thus it is seen that the prior art technique does not provide for timely updating of plant process data, particularly dynamic data.
Because of the foregoing, it is desirable to develop a display update system which provides for minimum time required for display of critical plant process dynamic data.